用杰克逊解析巨大的JSON

Question

Consider a huge JSON with structure like -

{"text": "very HUGE text here.."}

I am storing this JSON as an ObjectNode object called say json .

Now I try to extract this text from the ObjectNode .

String text = json.get("text").asText()

This JSON can be like 4-5 MB in size. When I run this code, I dont get a result (program keeps executing forever).

The above method works fine for small and normal sized strings. Is there any other best practice to extract huge data from JSON?

Answer 1

test with jackson(fastxml), 7MB json node can be parsed in 200 milliseconds

    ObjectMapper objectMapper = new ObjectMapper();
    InputStream is = getClass().getResourceAsStream("/test.json");
    long begin = System.currentTimeMillis();
    Map<String,String> obj = objectMapper.readValue(is, HashMap.class);
    long end = System.currentTimeMillis();
    System.out.println(obj.get("value").length() + "\t" + (end - begin));

the output is: 7888888 168

try to upgrade you jackson?

Answer 2

Perhaps your default heap size is too small: if input is 5 megs UTF-8 encoded, Java String of it will usually need 10 megs of memory ( char is 16-bits, most UTF-8 for english chars is single byte). There isn't much you can do about this, regardless of JSON library, if value has to be handled as Java String ; you need enough memory for the value and rest of processing. Further, since Java heap is divided into different generations, 64 megs may or may not work: since 10 megs needs to be consecutive, it probably gets allocated in the old generation.

So: see try with bigger heap size and see how much you need.